Collecting posture and activity information to evaluate therapy

ABSTRACT

A medical device, programmer, or other computing device may determine values of one or more activity and, in some embodiments, posture metrics for each therapy parameter set used by the medical device to deliver therapy. The metric values for a parameter set are determined based on signals generated by the sensors when that therapy parameter set was in use. Activity metric values may be associated with a postural category in addition to a therapy parameter set, and may indicate the duration and intensity of activity within one or more postural categories resulting from delivery of therapy according to a therapy parameter set. A posture metric for a therapy parameter set may indicate the fraction of time spent by the patient in various postures when the medical device used a therapy parameter set. The metric values may be used to evaluate the efficacy of the therapy parameter sets.

This application is a continuation of U.S. application Ser. No.11/691,381, filed Mar. 26, 2007, which is a continuation-in-part of U.S.application Ser. No. 11/106,051, filed Apr. 14, 2005, which claimed thebenefit of U.S. provisional application No. 60/562,024, filed Apr. 14,2004. U.S. application Ser. no. 11/691,381 also claims the benefit ofU.S. provisional application no. 60/785,677, filed Mar. 24, 2006. Theentire content of each of these applications is incorporated herein byreference.

TECHNICAL FIELD

The invention relates to medical devices and, more particularly, tomedical devices that deliver therapy.

BACKGROUND

In some cases, an ailment may affect a patient's activity level or rangeof activities by preventing the patient from being active. For example,chronic pain may cause a patient to avoid particular physicalactivities, or physical activity in general, where such activitiesincrease the pain experienced by the patient. Other ailments that mayaffect patient activity include movement disorders, such as tremor,Parkinson's disease, multiple sclerosis, epilepsy, or spasticity, whichmay result in irregular movement or activity, as well as a generallydecreased level of activity. The difficulty walking or otherwise movingexperienced by patients with movement disorders may cause such patientsto avoid movement to the extent possible. Further, depression, mania,bipolar disorder, obsessive-compulsive disorder, or other psychologicaldisorders, and congestive heart failure, cardiac arrhythmia,gastrointestinal disorders, and incontinence are other examples ofdisorders that may generally cause a patient to be less active. When apatient is inactive, he may be more likely to be recumbent, i.e., lyingdown, or sitting, and may change postures less frequently. Any of avariety of neurological disorders, including movement disorders,psychological disorders and chronic pain, may negatively patientactivity and/or posture.

In some cases, these ailments are treated via a medical device, such asan implantable medical device (IMD). For example, patients may receivean implantable neurostimulator or drug delivery device to treat chronicpain, a movement disorder, or a psychological disorder. Congestive heartfailure may be treated by, for example, a cardiac pacemaker or a drugdelivery device.

SUMMARY

In general, the invention is directed to techniques for evaluating atherapy delivered to a patient by a medical device based on patientactivity, posture, or both. At any given time, the medical devicedelivers the therapy according to a current set of therapy parameters.The therapy parameters may be changed over time such that the therapy isdelivered according to a plurality of different therapy parameter sets.The invention may provide techniques for evaluating the relativeefficacy of the plurality of therapy parameter sets.

A system according to the invention may include a medical device thatdelivers therapy to a patient, one or more programmers or othercomputing devices that communicate with the medical device, and one ormore sensors that generate signals as a function of at least one ofpatient activity and posture. The medical device, programmer, or othercomputing device may determine values of one or more activity metricsand, in some embodiments, may also determine posture metric values foreach therapy parameter set used by the medical device to delivertherapy. The activity and posture metric values for a therapy parameterset are determined based on the signals generated by the sensors whenthat therapy parameter set was in use. The activity metric value mayindicate a level of activity when the medical device used a particulartherapy parameter set. Activity metric values may be associated with apostural category in addition to a therapy parameter set, and mayindicate the duration and intensity of activity within one or morepostural categories resulting from delivery of therapy according to atherapy parameter set. A posture metric value for a therapy parameterset may indicate the fraction of time spent by the patient in variouspostures when the medical device used a particular therapy parameterset.

The therapy and subsequent evaluation of therapy may be directed totreating any number of disorders. For example, the therapy may bedirected to treating a non-respiratory neurological disorder, such as amovement disorder or psychological disorder. Example movement disordersfor which therapy may be provided are Parkinson's disease, essentialtremor and epilepsy. Non-respiratory neurological disorders do notinclude respiratory disorders, such as sleep apnea.

A clinician may use the one or more activity or posture metric values toevaluate therapy parameter sets used by the medical device to delivertherapy, or a sensitivity analysis may identify one or more potentiallyefficacious therapy parameter sets based on the metric values. In eithercase, the activity and/or posture metric values may be used to evaluatethe relative efficacy of the parameter sets, and the parameter sets thatsupport the highest activity levels and most upright and active posturesfor the patient may be readily identified.

In one embodiment, the invention is directed to a method in which aplurality of signals are monitored. Each of the signals is generated bya sensor as a function of at least one of activity or posture of apatient. A posture of the patient is periodically identified based on atleast one of the signals, and each of the identified postures isassociated with a therapy parameter set currently used by a medicaldevice to deliver a therapy to a patient when the posture is identified.An activity level of the patient is periodically determined based on atleast one of the signals, and each of the determined activity levels isassociated with a therapy parameter set currently used by a medicaldevice to deliver a therapy to a patient when the activity level isidentified, and with a current one of the periodically identifiedpostures. For each of a plurality of therapy parameter sets used by themedical device to deliver therapy to the patient, a value of an activitymetric may be determined for each of the periodically identifiedpostures associated with the therapy parameter set based on the activitylevels associated with the posture and the therapy parameter set.

In another embodiment, the invention is directed to medical systemcomprising a plurality of sensors, each of the sensors generating asignal as a function of at least one of activity or posture of apatient, a medical device that delivers a therapy to the patient, and aprocessor. The processor monitors the signals generated by the sensors,periodically identifies a posture of the patient based on at least oneof the signals, associates each of the identified postures with atherapy parameter set currently used by a medical device to deliver atherapy to a patient when the posture is identified, periodicallydetermines an activity level of the patient based on at least one of thesignals, associates each of the determined activity levels with atherapy parameter set currently used by a medical device to deliver atherapy to a patient when the activity level is determined and a currentone of the periodically identified postures, and, for each of aplurality of therapy parameter sets used by the medical device todeliver therapy to the patient, determines a value of an activity metricfor each of the periodically identified postures associated with thetherapy parameter set based on the activity levels associated with theposture and the therapy parameter set.

In another embodiment, the invention is directed to a computer-readablemedium comprising instructions. The instructions cause a programmableprocessor to monitor a plurality of signals, each of the signalsgenerated by a sensor as a function of at least one of activity orposture of a patient. The instructions further cause the processor toperiodically identify a posture of the patient based on at least one ofthe signals, and associate each of the identified postures with atherapy parameter set currently used by a medical device to deliver atherapy to a patient when the posture is identified. The instructionsfurther cause the processor to periodically determine an activity levelof the patient based on at least one of the signals, and associate eachof the determined activity levels with a therapy parameter set currentlyused by a medical device to deliver a therapy to a patient when theactivity level is determined and a current one of the periodicallyidentified postures. The instructions further cause the processor to,for each of a plurality of therapy parameter sets used by the medicaldevice to deliver therapy to the patient, determine a value of anactivity metric for each of the periodically identified posturesassociated with the therapy parameter set based on the activity levelsassociated with the posture and the therapy parameter set.

The invention is capable of providing one or more advantages. Forexample, a medical system according to the invention may provide aclinician with an objective indication of the efficacy of different setsof therapy parameters. The indication of efficacy may be provided interms of the ability of the patient to assume particular postures andactivity levels for each given set of therapy parameters, permittingidentification of particular sets of therapy parameters that yield thehighest efficacy. Further, a medical device, programming device, orother computing device according to the invention may display therapyparameter sets and associated metric values in an ordered and, in somecases, sortable list, which may allow the clinician to more easilycompare the relative efficacies of a plurality of therapy parametersets. The medical system may be particularly useful in the context oftrial neurostimulation for treatment of chronic pain or movementdisorders, where the patient is encouraged to try a plurality of therapyparameter sets to allow the patient and clinician to identifyefficacious therapy parameter sets. Further, in some embodiments, thesystem may provide at least semi-automated identification of potentiallyefficacious therapy parameter sets, through application of a sensitivityanalysis to one or more activity or posture metrics.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A and 1B are conceptual diagrams illustrating example systemsthat include an implantable medical device that collects posture andactivity information according to the invention.

FIGS. 2A and 2B are block diagrams further illustrating the examplesystems and implantable medical devices of FIGS. 1A and 1B.

FIG. 3 is a logic diagram illustrating an example circuit that detectsthe sleep state of a patient from the electroencephalogram (EEG) signal.

FIG. 4 is a block diagram illustrating an example memory of theimplantable medical device of FIG. 1.

FIG. 5 is a flow diagram illustrating an example method for collectingposture and activity information that may be employed by an implantablemedical device.

FIG. 6 is a flow diagram illustrating an example method for collectingactivity information based on patient posture that may be employed by animplantable medical device.

FIG. 7 is a block diagram illustrating an example clinician programmer.

FIG. 8 illustrates an example list of therapy parameter sets andassociated posture and activity metric values that may be presented by aclinician programmer.

FIG. 9 is a flow diagram illustrating an example method for displaying alist of therapy parameter sets and associated posture and activitymetric values that may be employed by a clinician programmer.

FIG. 10 is a flow diagram illustrating an example method for identifyinga therapy parameter set based on collected posture and/or activityinformation that may be employed by a medical device.

FIG. 11 is a conceptual diagram illustrating a monitor that monitorsvalues of one or more physiological parameters of the patient.

FIG. 12 is a conceptual diagram illustrating a monitor that monitorssignals generated by one or more accelerometers disposed on the patient.

FIG. 13 is a flow diagram illustrating an example technique formonitoring the heart rate and breathing rate of a patient by measuringcerebral spinal fluid pressure.

DETAILED DESCRIPTION

FIGS. 1A and 1B are conceptual diagrams illustrating example systems 10Aand 10B (collectively “systems 10”) that respectively include animplantable medical device (IMD) 14A or 14B (collectively “IMDs 14”)that collect information relating to the activity and, in someembodiments, the posture of a respective one or patients 12A and 12B(collectively “patients 12”). In the illustrated example systems 10,IMDs 14 takes the form of an implantable neurostimulators that deliverneurostimulation therapy in the form of electrical pulses to patients12. However, the invention is not limited to implementation via animplantable neurostimulator. For example, in some embodiments of theinvention, IMDs 14 may take the form of an implantable pump orimplantable cardiac rhythm management device, such as a pacemaker, thatcollects activity and posture information. Further, the invention is notlimited to implementation via an IMD. In other words, any implantable orexternal medical device may collect activity and posture informationaccording to the invention.

In the example of FIGS. 1A and 1B, IMDs 14 deliver neurostimulationtherapy to patient 12A via leads 16A and 16B, and leads 16C and 16D(collectively “leads 16”), respectively. Leads 16A and 16B may, as shownin FIG. 1A, be implanted proximate to the spinal cord 18 of patient 12A,and IMD 14A may deliver spinal cord stimulation (SCS) therapy to patient12A in order to, for example, reduce pain experienced by patient 12A.However, the invention is not limited to the configuration of leads 16Aand 16B shown in FIG. 1A or the delivery of SCS or other pain therapies.

For example, in another embodiment, illustrated in FIG. 1B, leads 16Cand 16D may extend to brain 19 of patient 12B, e.g., through cranium 17of patient. IMD 14B may deliver deep brain stimulation (DBS) or corticalstimulation therapy to patient 12 to treat any of a variety ofnon-respiratory neurological disorders, such as movement disorders orpsychological disorders. Example therapies may treat tremor, Parkinson'sdisease, spasticity, epilepsy, depression or obsessive-compulsivedisorder. As illustrated in FIG. 1B, leads 16C and 16D may be coupled toIMD 14B via one or more lead extensions 15.

As further examples, one or more leads 16 may be implanted proximate tothe pelvic nerves (not shown) or stomach (not shown), and an IMD 14 maydeliver neurostimulation therapy to treat incontinence or gastroparesis.Additionally, leads 16 may be implanted on or within the heart to treatany of a variety of cardiac disorders, such as congestive heart failureor arrhythmia, or may be implanted proximate to any peripheral nerves totreat any of a variety of disorders, such as peripheral neuropathy orother types of chronic pain.

The illustrated numbers and locations of leads 16 are merely examples.Embodiments of the invention may include any number of leads implantedat any of a variety of locations within a patient. Furthermore, theillustrated number and location of IMDs 14 are merely examples. IMDs 14may be located anywhere within patient according to various embodimentsof the invention. For example, in some embodiments, an IMD 14 may beimplanted on or within cranium 17 for delivery of therapy to brain 19,or other structure of the head of the patient 12.

IMDs 14 deliver therapy according to a set of therapy parameters, i.e.,a set of values for a number of parameters that define the therapydelivered according to that therapy parameter set. In embodiments whereIMDs 14 deliver neurostimulation therapy in the form of electricalpulses, the parameters in each parameter set may include voltage orcurrent pulse amplitudes, pulse widths, pulse rates, duration, dutycycle and the like. Further, each of leads 16 includes electrodes (notshown in FIGS. 1A and 1B), and a therapy parameter set may includeinformation identifying which electrodes have been selected for deliveryof pulses, and the polarities of the selected electrodes. In embodimentsin which IMDs 14 deliver other types of therapies, therapy parametersets may include other therapy parameters such as drug concentration anddrug flow rate in the case of drug delivery therapy. Therapy parametersets used by IMDs 14 may include a number of parameter sets programmedby a clinician (not shown), and parameter sets representing adjustmentsmade by patients 12 to these preprogrammed sets.

Each of systems 10 may also include a clinician programmer 20(illustrated as part of system 10A in FIG. 1A). The clinician may useclinician programmer 20 to program therapy for patient 12A, e.g.,specify a number of therapy parameter sets and provide the parametersets to IMD 14A. The clinician may also use clinician programmer 20 toretrieve information collected by IMD 14A. The clinician may useclinician programmer 20 to communicate with IMD 14A both during initialprogramming of IMD 14A, and for collection of information and furtherprogramming during follow-up visits.

Clinician programmer 20 may, as shown in FIG. 1A, be a handheldcomputing device. Clinician programmer 20 includes a display 22, such asa LCD or LED display, to display information to a user. Clinicianprogrammer 20 may also include a keypad 24, which may be used by a userto interact with clinician programmer 20. In some embodiments, display22 may be a touch screen display, and a user may interact with clinicianprogrammer 20 via display 22. A user may also interact with clinicianprogrammer 20 using peripheral pointing devices, such as a stylus ormouse. Keypad 24 may take the form of an alphanumeric keypad or areduced set of keys associated with particular functions.

Systems 10 may also include a patient programmer 26 (illustrated as partof system 10A in FIG. 1A), which also may, as shown in FIG. 1A, be ahandheld computing device. Patient 12A may use patient programmer 26 tocontrol the delivery of therapy by IMD 14A. For example, using patientprogrammer 26, patient 12A may select a current therapy parameter setfrom among the therapy parameter sets preprogrammed by the clinician, ormay adjust one or more parameters of a preprogrammed therapy parameterset to arrive at the current therapy parameter set.

Patient programmer 26 may include a display 28 and a keypad 30, to allowpatient 12A to interact with patient programmer 26. In some embodiments,display 26 may be a touch screen display, and patient 12A may interactwith patient programmer 26 via display 28. Patient 12A may also interactwith patient programmer 26 using peripheral pointing devices, such as astylus, mouse, or the like.

Clinician and patient programmers 20, 26 are not limited to thehand-held computer embodiments illustrated in FIG. 1A. Programmers 20,26 according to the invention may be any sort of computing device. Forexample, a programmer 20, 26 according to the invention may be atablet-based computing device, a desktop computing device, or aworkstation.

IMD 14A, clinician programmer 20 and patient programmer 26 may, as shownin FIG. 1A, communicate via wireless communication. Clinician programmer20 and patient programmer 26 may, for example, communicate via wirelesscommunication with IMD 14A using radio frequency (RF) or infraredtelemetry techniques known in the art. Clinician programmer 20 andpatient programmer 26 may communicate with each other using any of avariety of local wireless communication techniques, such as RFcommunication according to the 802.11 or Bluetooth specification sets,infrared communication according to the IRDA specification set, or otherstandard or proprietary telemetry protocols.

Clinician programmer 20 and patient programmer 26 need not communicatewirelessly, however. For example, programmers 20 and 26 may communicatevia a wired connection, such as via a serial communication cable, or viaexchange of removable media, such as magnetic or optical disks, ormemory cards or sticks. Further, clinician programmer 20 may communicatewith one or both of IMD 14 and patient programmer 26 via remotetelemetry techniques known in the art, communicating via a local areanetwork (LAN), wide area network (WAN), public switched telephonenetwork (PSTN), or cellular telephone network, for example.

As mentioned above, an IMD 14 collects patient activity information.Specifically, as will be described in greater detail below, an IMD 14periodically determines an activity level of a patient 12 based on asignal that varies as a function of patient activity. An activity levelmay comprise, for example, a number of activity counts, or a value for aphysiological parameter that reflects patient activity.

In some embodiments, an IMD 14 also collects patient postureinformation. In such embodiments, an IMD 14 may monitor one or moresignals that vary as a function of patient posture, and may identifypostures based on the signals. An IMD 14 may, for example, periodicallyidentify the posture of a patient 12 or transitions between posturesmade by the patient 12. For example, an IMD 14 may identify whether thepatient is upright or recumbent, e.g., lying down, whether the patientis standing, sitting, or recumbent, or transitions between suchpostures.

In exemplary embodiments, as will be described in greater detail below,an IMD 14 monitors the signals generated by a plurality ofaccelerometers. In such embodiments, an IMD 14 may both determineactivity levels and identify postures or postural transitions based onthe accelerometer signals. Specifically, an IMD 14 may compare the DCcomponents of the accelerometer signals to one or more thresholds toidentify postures, and may compare a non-DC portion of one or more ofthe signals to one or more thresholds to determine activity levels.

Over time, an IMD 14 may use a plurality of different therapy parametersets to deliver the therapy to a patient 12. In some embodiments, an IMD14 associates each determined posture with the therapy parameter setthat is currently active when the posture is identified. In suchembodiments, an IMD 14 may also associate each determined activity levelwith the currently identified posture, and with the therapy parameterset that is currently active when the activity level is determined. Inother embodiments, an IMD 14 may use posture to control whether activitylevels are monitored. In such embodiments, an IMD 14 determines whethera patient 12 is in a target posture, e.g., a posture of interest such asupright or standing, and determines activity levels for association withcurrent therapy parameter sets during periods when the patient is in thetarget posture.

In either case, an IMD 14 may determine at least one value of one ormore activity metrics for each of the plurality of therapy parametersets based on the activity levels associated with the therapy parametersets. An activity metric value may be, for example, a mean or medianactivity level, such as an average number of activity counts per unittime. In other embodiments, an activity metric value may be chosen froma predetermined scale of activity metric values based on a comparison ofa mean or median activity level to one or more threshold values. Thescale may be numeric, such as activity metric values from 1-10, orqualitative, such as low, medium or high activity.

In some embodiments, each activity level associated with a therapyparameter set is compared with the one or more thresholds, andpercentages of time above and/or below the thresholds are determined asone or more activity metric values for that therapy parameter set. Inother embodiments, each activity level associated with a therapyparameter set is compared with a threshold, and an average length oftime that consecutively determined activity levels remain above thethreshold is determined as an activity metric value for that therapyparameter set.

In embodiments in which an IMD 14 associates identified postures withthe current therapy parameter set, and associates each determinedactivity level with a current posture and the current therapy parameterset, the IMD 14 may, for each therapy parameter set, identify theplurality of postures assumed by a patient 12 when that therapyparameter set was in use. An IMD 14 may then determine a value of one ormore activity metrics for each therapy parameter set/posture pair basedon the activity levels associated with that therapy parameterset/posture pair.

Further, for each therapy parameter set, an IMD 14 may also determine avalue of one or more posture metrics based on the postures or posturaltransitions associated with that therapy parameter set. A posture metricvalue may be, for example, an amount or percentage of time spent in aposture while a therapy parameter set is active, e.g., an average amountof time over a period of time, such as an hour, that a patient 12 waswithin a particular posture. In some embodiments, a posture metric valuemay be an average number of posture transitions over a period of time,e.g., an hour.

In some embodiments, a plurality of activity metric values aredetermined for each of the plurality of therapy parameter sets, orparameter set/posture pairs. In such embodiments, an overall activitymetric value may be determined. For example, the plurality of individualactivity metric values may be used as indices to identify an overallactivity metric value from a look-up table. The overall activity metricmay be selected from a predetermined scale of activity metric values,which may be numeric, such as activity metric values from 1-10, orqualitative, such as low, medium or high activity.

Similarly, in some embodiments, a plurality of posture metric values isdetermined for each of the plurality of therapy parameter sets. In suchembodiments, an overall posture metric value may be determined. Forexample, the plurality of individual posture metric values may be usedas indices to identify an overall posture metric value from a look-uptable. The overall posture metric may be selected from a predeterminedscale of posture metric values, which may be numeric, such as posturemetric values from 1-10.

Although described herein primarily with reference to an IMD 14, one ormore of the IMD 14, clinician programmer 20, patient programmer 26, oranother computing device may determine activity and posture metricvalues in the manner described herein with reference to the IMD 14. Forexample, in some embodiments, an IMD 14 determines and stores metricvalues, and provides information identifying therapy parameter sets andthe metric values associated with the therapy parameter sets, to one orboth of programmers 20, 26. In other embodiments, an IMD 14 providesinformation identifying the therapy parameter sets and associatedposture events and activity levels to one or both of programmers 20, 26,or another computing device, and the programmer or other computingdevice determines activity and posture metric values for each of thetherapy parameter sets.

In either of these embodiments, programmers 20, 26 or the othercomputing device may present information to a user that may be used toevaluate the therapy parameter sets based on the activity and posturemetric values. For ease of description, the presentation of informationthat may be used to evaluate therapy parameter sets will be describedhereafter with reference to embodiments in which clinician programmer 20presents information to a clinician. However, it is understood that, insome embodiments, patient programmer 26 or another computing device maypresent such information to a user, such as a clinician or a patient 12.

For example, in some embodiments, clinician programmer 20 may present alist of the plurality of parameter sets and associated posture andactivity metric values to the clinician via display 22. Where values aredetermined for a plurality of posture and activity metrics for each ofthe therapy parameter sets, programmer 20 may order the list accordingto the values of one of the metrics that is selected by the clinician.Programmer 20 may also present other activity and/or posture informationto the clinician, such as graphical representations of activity and/orposture. For example, programmer 20 may present a trend diagram ofactivity or posture over time, or a histogram or pie chart illustratingpercentages of time that activity levels were within certain ranges orthat a patient 12 assumed certain postures. Programmer 20 may generatesuch charts or diagrams using activity levels or posture eventsassociated with a particular one of the therapy parameter sets, or allof the activity levels and posture events determined by an IMD 14.

However, the invention is not limited to embodiments that includeprogrammers 20, 26 or another computing device, or embodiments in whicha programmer or other computing device presents posture and activityinformation to a user. For example, in some embodiments, an externalmedical device comprises a display. In such embodiments, the externalmedical device both determines the metric values for the plurality oftherapy parameter sets, and presents the list of therapy parameter setsand associated metric values.

Further, the invention is not limited to embodiments in which a medicaldevice determines activity levels or identifies postures. For example,in some embodiments, an IMD 14 may instead periodically record samplesof one or more signals, and associate the samples with a current therapyparameter set. In such embodiments, a programmer 20, 26 or anothercomputing device may receive information identifying a plurality oftherapy parameter sets and the samples associated with the parametersets, determine activity levels and identify postures and posturaltransitions based on the samples, and determine one or more activityand/or posture metric values for each of the therapy parameter setsbased on the determined activity levels and identified postures.

Moreover, the invention is not limited to embodiments in which thetherapy delivering medical device includes or is coupled to the sensorsthat generate a signal as a function of patient activity or posture. Insome embodiments, systems 10 may include a separate implanted orexternal monitor that includes or is coupled to such sensors. Themonitor may provide samples of the signals generated by such sensors tothe IMD, programmers or other computing device for determination ofactivity levels, postures, activity metric values and posture metricvalues as described herein.

The monitor may provide the samples in real-time, or may record samplesfor later transmission. In embodiments where the monitor records thesamples for later transmission, the monitor may associate the sampleswith the time they were recorded. In such embodiments, an IMD 14 mayperiodically record indications of a currently used therapy parameterset and the current time. Based on the association of recorded signalsamples and therapy parameter sets with time, the recorded signalsamples may be associated with current therapy parameter sets fordetermination of activity and posture metric values as described herein.

In some embodiments, in addition to, or as an alternative to thepresentation of information to a clinician for evaluation of therapyparameter sets, one or more of an IMD 14, programmers 20, 26, or anothercomputing device may identify therapy parameter sets for use in deliveryof therapy to a patient 12 based on a sensitivity analysis of one ormore activity and/or posture metrics. The sensitivity analysisidentifies values of therapy parameters that define a substantiallymaximum or minimum value of the one or more metrics. In particular, aswill be described in greater detail below, one or more of an IMD 14 andprogrammers 20, 26 conducts the sensitivity analysis of the one or moremetrics, and identifies at least one baseline therapy parameter set thatincludes the values for individual therapy parameters that wereidentified based on the sensitivity analysis. An IMD 14 may deliverytherapy according to the baseline therapy parameter set. Furthermore,one or more of an IMD 14 and programmers 20, 26 may periodically perturbat least one therapy parameter value of the baseline therapy parameterset to determine whether the baseline therapy parameter set stilldefines a substantially maximum or minimum value of the one or moremetrics. If the baseline therapy parameter set no longer defines asubstantially maximum or minimum value of the one or more metrics, asearch may be performed to identify a new baseline therapy parameter setfor use in delivery of therapy to a patient 12.

FIGS. 2A and 2B are block diagrams further illustrating systems 10A and10B. In particular, FIG. 2A illustrates an example configuration of IMD14A and leads 16A and 16B. FIG. 2B illustrates an example configurationof IMD 14B and leads 16C and 16D. FIGS. 2A and 2B also illustratesensors 40A and 40B (collectively “sensors 40”) that generate signalsthat vary as a function of patient activity and/or posture. As will bedescribed in greater detail below, IMDs 14 monitor the signals, and mayperiodically identify the posture of patients 12 and determine anactivity level based on the signals.

IMD 14A may deliver neurostimulation therapy via electrodes 42A-D oflead 16A and electrodes 42E-H of lead 16B, while IMD 14B deliversneurostimulation via electrodes 42I-L of lead 16C and electrodes 42 M-Pof lead 16D (collectively “electrodes 40”). Electrodes 40 may be ringelectrodes. The configuration, type and number of electrodes 40illustrated in FIGS. 2A and 2B are merely exemplary. For example, leads16 may each include eight electrodes 40, and the electrodes 42 need notbe arranged linearly on each of leads 16.

In each of systems 10A and 10B, electrodes 42 are electrically coupledto a therapy delivery module 44 via leads 16. Therapy delivery module 44may, for example, include an output pulse generator coupled to a powersource such as a battery. Therapy delivery module 44 may deliverelectrical pulses to a patient 12 via at least some of electrodes 42under the control of a processor 46, which controls therapy deliverymodule 44 to deliver neurostimulation therapy according to a currenttherapy parameter set. However, the invention is not limited toimplantable neurostimulator embodiments or even to IMDs that deliverelectrical stimulation. For example, in some embodiments a therapydelivery module 44 of an IMD may include a pump, circuitry to controlthe pump, and a reservoir to store a therapeutic agent for delivery viathe pump.

Processor 46 may include a microprocessor, a controller, a digitalsignal processor (DSP), an application specific integrated circuit(ASIC), a field-programmable gate array (FPGA), discrete logiccircuitry, or the like. Memory 48 may include any volatile,non-volatile, magnetic, optical, or electrical media, such as a randomaccess memory (RAM), read-only memory (ROM), non-volatile RAM (NVRAM),electrically-erasable programmable ROM (EEPROM), flash memory, and thelike. In some embodiments, memory 48 stores program instructions that,when executed by processor 46, cause IMD 14 and processor 46 to performthe functions attributed to them herein.

Each of sensors 40 generates a signal that varies as a function ofpatient activity and/or posture. An IMD 14 may include circuitry (notshown) that conditions the signals generated by sensors 40 such thatthey may be analyzed by processor 46. For example, an IMD 14 may includeone or more analog to digital converters to convert analog signalsgenerated by sensors 40 into digital signals usable by processor 46, aswell as suitable filter and amplifier circuitry. Although shown asincluding two sensors 40, systems 10A and 10B may include any number ofsensors.

Further, as illustrated in FIGS. 2A and 2B, sensors 40 may be includedas part of IMDs 14, or coupled to IMDs 14 via leads 16. Sensors 40 maybe coupled to IMD 14 via therapy leads 16A-16D, or via other leads 16,such as lead 16E depicted in FIGS. 2A and 2B. In some embodiments, asensor 40 located outside of an IMD 14 may be in wireless communicationwith processor 46. Wireless communication between sensors 40 and IMDs 14may, as examples, include RF communication or communication viaelectrical signals conducted through the tissue and/or fluid of apatient 12.

In exemplary embodiments, sensors 40 include a plurality ofaccelerometers, e.g., three accelerometers, which are orientedsubstantially orthogonally with respect to each other. In addition tobeing oriented orthogonally with respect to each other, each ofaccelerometers may be substantially aligned with an axis of the body ofa patient 12. The magnitude and polarity of DC components of the signalsgenerated by the accelerometers indicate the orientation of the patientrelative to the Earth's gravity, and processor 46 may periodicallyidentify the posture or postural changes of a patient 12 based on themagnitude and polarity of the DC components. Further informationregarding use of orthogonally aligned accelerometers to determinepatient posture may be found in a commonly assigned U.S. Pat. No.5,593,431, which issued to Todd J. Sheldon.

Processor 46 may periodically determine the posture of a patient 12, andmay store indications of the determined postures within memory 48. Wherea system 10 includes a plurality of orthogonally aligned accelerometerslocated on or within the trunk of a patient 12, e.g., within an IMD 14which is implanted within the abdomen of the patient 12 as illustratedin FIGS. 1A and 1B, processor 46 may be able to periodically determinewhether patient is, for example, upright or recumbent, e.g., lying down.In embodiments of systems 10 that include an additional one or moreaccelerometers at other locations on or within the body of a patient 12,processor 46 may be able to identify additional postures of the patient12. For example, in an embodiment of systems 10 that includes one ormore accelerometers located on or within the thigh of a patient 12,processor 46 may be able to identify whether the patient 12 is standing,sitting, or lying down. Processor 46 may also identify transitionsbetween postures based on the signals output by the accelerometers, andmay store indications of the transitions, e.g., the time of transitions,within memory 48.

Processor 46 may identify postures and posture transitions by comparingthe signals generated by the accelerometers to one or more respectivethreshold values. For example, when a patient 12 is upright, a DCcomponent of the signal generated by one of the plurality oforthogonally aligned accelerometers may be substantially at a firstvalue, e.g., high or one, while the DC components of the signalsgenerated by the others of the plurality of orthogonally alignedaccelerometers may be substantially at a second value, e.g., low orzero. When a patient 12 becomes recumbent, the DC component of thesignal generated by one of the plurality of orthogonally alignedaccelerometers that had been at the second value when the patient wasupright may change to the first value, and the DC components of thesignals generated by others of the plurality of orthogonally alignedaccelerometers may remain at or change to the second value. Processor 46may compare the signals generated by such sensors to respectivethreshold values stored in memory 48 to determine whether they aresubstantially at the first or second value, and to identify when thesignals change from the first value to the second value.

Processor 46 may determine an activity level based on one or more of theaccelerometer signals by sampling the signals and determining a numberof activity counts during the sample period. For example, processor 46may compare the sample of a signal generated by an accelerometer to oneor more amplitude thresholds stored within memory 48, and may identifyeach threshold crossing as an activity count. Where processor 46compares the sample to multiple thresholds with varying amplitudes,processor 46 may identify crossing of higher amplitude thresholds asmultiple activity counts. Using multiple thresholds to identify activitycounts, processor 46 may be able to more accurately determine the extentof patient activity for both high impact, low frequency and low impact,high frequency activities. Processor 46 may store the determined numberof activity counts in memory 48 as an activity level. In someembodiments, an IMD 14 may include a filter (not shown), or processor 46may apply a digital filter, that passes a band of the accelerometersignal from approximately 0.1 Hz to 10 Hz, e.g., the portion of thesignal that reflects patient activity.

Processor 46 may identify postures and record activity levelscontinuously or periodically, e.g., one sample of the signals output bysensors 40 every minute or continuously for ten minutes each hour.Further, processor 46 need not identify postures and record activitylevels with the same frequency. For example, processor 46 may identifypostures less frequently then activity levels are determined.

In some embodiments, processor 46 limits recording of postures andactivity levels to relevant time periods, i.e., when a patient 12 isawake or likely to be awake, and therefore likely to be active. Forexample, a patient 12 may indicate via patient programmer 26 whenpatient is going to sleep or has awoken. Processor 46 may receive theseindications via a telemetry circuit 50 of an IMD 14, and may suspend orresume recording of posture events based on the indications. In otherembodiments, processor 46 may maintain a real-time clock, and may recordposture events based on the time of day indicated by the clock, e.g.,processor 46 may limit posture event recording to daytime hours.Alternatively, processor 46 may wirelessly interact with a real-timeclock within the patient programmer.

In some embodiments, processor 46 may monitor one or more physiologicalparameters of a patient 12 via signals generated by sensors 40, and maydetermine when the patient 12 is attempting to sleep or asleep based onthe physiological parameters. For example, processor 46 may determinewhen a patient 12 is attempting to sleep by monitoring the posture ofthe patient 12 to determine when the patient 12 is recumbent.

In order to determine whether a patient 12 is asleep, processor 46 maymonitor any one or more physiological parameters that discernibly changewhen the patient 12 falls asleep, such as activity level, heart rate,ECG morphological features, respiration rate, respiratory volume, bloodpressure, blood oxygen saturation, partial pressure of oxygen withinblood, partial pressure of oxygen within cerebrospinal fluid, muscularactivity and tone, core temperature, subcutaneous temperature, arterialblood flow, brain electrical activity, eye motion, and galvanic skinresponse. Processor 46 may additionally or alternatively monitor thevariability of one or more of these physiological parameters, such asheart rate and respiration rate, which may discernible change when apatient 12 is asleep. Further details regarding monitoring physiologicalparameters to identify when a patient is attempting to sleep and whenthe patient is asleep may be found in a commonly-assigned U.S. patentapplication Ser. No. 11/691,405 by Kenneth Heruth and Keith Miesel,entitled “DETECTING SLEEP,” which was filed Mar. 26, 2007, issued asU.S. Pat. No. 8,055,348 on Nov. 8, 2011, and is incorporated herein byreference in its entirety.

In some embodiments, processor 46 gates activity and posture monitoringbased on patient sleep. Further, in some embodiments, sensors 40 mayinclude one or more electrodes positioned within or proximate to thebrain of patient 12, which detect electrical activity of the brain. Forexample, in embodiments in which an IMD 14 delivers stimulation ortherapeutic agents to the brain, processor 46 may be coupled toelectrodes implanted on or within the brain via a lead 16. System 10B,illustrated in FIGS. 1B and 2B, is an example of a system that includeselectrodes 42, located on or within the brain of patient 12B, that arecoupled to IMD 14B.

As shown in FIG. 2B, electrodes 42 may be selectively coupled to therapymodule 44 or an EEG signal module 54 by a multiplexer 52, which operatesunder the control of processor 46. EEG signal module 54 receives signalsfrom a selected set of the electrodes 42 via multiplexer 52 ascontrolled by processor 46. EEG signal module 54 may analyze the EEGsignal for certain features indicative of sleep or different sleepstates, and provide indications of relating to sleep or sleep states toprocessor 46. Thus, electrodes 42 and EEG signal module 54 may beconsidered another sensor 40 in system 10B. IMD 14B may includecircuitry (not shown) that conditions the EEG signal such that it may beanalyzed by processor 52. For example, IMD 14B may include one or moreanalog to digital converters to convert analog signals received fromelectrodes 42 into digital signals usable by processor 46, as well assuitable filter and amplifier circuitry.

In some embodiments, processor 46 will only request EEG signal module 54to operate when one or more other physiological parameters indicate thatpatient 12B is already asleep. However, processor 46 may also direct EEGsignal module to analyze the EEG signal to determine whether patient 12Bis sleeping, and such analysis may be considered alone or in combinationwith other physiological parameters to determine whether patient 12B isasleep. EEG signal module 60 may process the EEG signals to detect whenpatient 12 is asleep using any of a variety of techniques, such astechniques that identify whether a patient is asleep based on theamplitude and/or frequency of the EEG signals. In some embodiments, thefunctionality of EEG signal module 54 may be provided by processor 46,which, as described above, may include one or more microprocessors,ASICs, or the like.

In other embodiments, processor 46 may record postures and activitylevels in response to receiving an indication from a patient 12 viapatient programmer 26. For example, processor 46 may record postures andactivity levels during times when a patient 12 believes the therapydelivered by an IMD 14 is ineffective and/or the symptoms experienced bythe patient 12 have worsened. In this manner, processor 46 may limitdata collection to periods in which more probative data is likely to becollected, and thereby conserve a battery and/or storage space withinmemory 48.

Although described above with reference to an exemplary embodiment inwhich sensors 40 include accelerometers, sensors 40 may include any of avariety of types of sensors that generate signals as a function ofpatient posture and/or activity. For example, sensors 40 may includeorthogonally aligned gyros or magnetometers that generate signals thatindicate the posture of a patient 12.

Other sensors 40 that may generate a signal that indicates the postureof a patient 12 include electrodes that generate an electromyogram (EMG)signal, or bonded piezoelectric crystals that generate a signal as afunction of contraction of muscles. Such sensors 40 may be implanted inthe legs, buttocks, abdomen, or back of a patient 12, as describedabove. The signals generated by such sensors when implanted in theselocations may vary based on the posture of a patient 12, e.g., may varybased on whether the patient is standing, sitting, or lying down.

Further, the posture of a patient 12 may affect the thoracic impedanceof the patient. Consequently, sensors 40 may include an electrode pair,including one electrode integrated with the housing of an IMD 14 and oneof electrodes 42, that generates a signal as a function of the thoracicimpedance of a patient 12, and processor 46 may detect the posture orposture changes of the patient 12 based on the signal. The electrodes ofthe pair may be located on opposite sides of the patient's thorax. Forexample, the electrode pair may include one of electrodes 42 locatedproximate to the spine of a patient for delivery of SCS therapy, and anIMD 14 with an electrode integrated in its housing may be implanted inthe abdomen of a patient 12.

Additionally, changes of the posture of a patient 12 may cause pressurechanges with the cerebrospinal fluid (CSF) of the patient. Consequently,sensors 40 may include pressure sensors coupled to one or moreintrathecal or intracerebroventricular catheters, or pressure sensorscoupled to an IMD 14 wirelessly or via leads 16. CSF pressure changesassociated with posture changes may be particularly evident within thebrain of the patient, e.g., may be particularly apparent in anintracranial pressure (ICP) waveform.

Other sensors 40 that output a signal as a function of patient activitymay include one or more bonded piezoelectric crystals, mercury switches,or gyros that generate a signal as a function of body motion, footfallsor other impact events, and the like. Additionally or alternatively,sensors 40 may include one or more electrodes that generate anelectromyogram (EMG) signal as a function of muscle electrical activity,which may indicate the activity level of a patient. The electrodes maybe, for example, located in the legs, abdomen, chest, back or buttocksof a patient 12 to detect muscle activity associated with walking,running, or the like. The electrodes may be coupled to an IMD 14wirelessly or by leads 16 or, if the IMD 14 is implanted in theselocations, integrated with a housing of the IMD 14.

However, bonded piezoelectric crystals located in these areas generatesignals as a function of muscle contraction in addition to body motion,footfalls or other impact events. Consequently, use of bondedpiezoelectric crystals to detect activity of a patient 12 may bepreferred in some embodiments in which it is desired to detect muscleactivity in addition to body motion, footfalls, or other impact events.Bonded piezoelectric crystals may be coupled to an IMD 14 wirelessly orvia leads 16, or piezoelectric crystals may be bonded to the can of theIMD 14 when the IMD is implanted in these areas, e.g., in the back,chest, buttocks or abdomen of a patient 12.

Further, in some embodiments, processor 46 may monitor one or moresignals that indicate a physiological parameter of a patient 12, whichin turn varies as a function of patient activity. For example, processor46 may monitor a signal that indicates the heart rate, ECG morphology,respiration rate, respiratory volume, core or subcutaneous temperature,or muscular activity of the patient, and sensors 40 may include anyknown sensors that output a signal as a function of one or more of thesephysiological parameters. In such embodiments, processor 46 mayperiodically determine a heart rate, value of an ECG morphologicalfeature, respiration rate, respiratory volume, core temperature, ormuscular activity level of a patient 12 based on the signal. Thedetermined values of these parameters may be mean or median values.

In some embodiments, processor 46 compares a determined value of such aphysiological parameter to one or more thresholds or a look-up tablestored in memory to determine a number of activity counts, and storesthe determined number of activity counts in memory 48 as a determinedactivity level. In other embodiments, processor 46 may store thedetermined physiological parameter value as a determined activity level.The use of activity counts, however, may allow processor 46 to determinean activity level based on a plurality of signals generated by aplurality of sensors 40. For example, processor 46 may determine a firstnumber of activity counts based on a sample of an accelerometer signaland a second number of activity counts based on a heart rate determinedfrom an electrogram signal at the time the accelerometer signal wassampled. Processor 46 may determine an activity level by calculating thesum or average, which may be a weighted sum or average, of first andsecond activity counts.

As described above, the invention is not limited to embodiments in whichan IMD 14 determines postures or activity levels. In some embodiments,processor 46 may periodically store samples of the signals generated bysensors 40 in memory 48, rather than postures and activity levels, andmay associate those samples with the current therapy parameter set.

FIG. 3 is a logical diagram of an example circuit that detects the sleepand/or sleep type of a patient based on the electroencephalogram (EEG)signal. Module 49, shown in FIG. 3, may be integrated into an EEG signalmodule 54 of IMD 14B, or some other implantable or external devicecapable of detecting an EEG signal according to other embodiments of theinvention. In such embodiments, module 49 may be used to, for example,determine whether a patient 12 is asleep, or in which sleep state thepatient is.

An EEG signal detected by electrodes 42 adjacent to the brain 19 ofpatent 12B is transmitted into module 49 and provided to three channels,each of which includes a respective one of amplifiers 51, 67 and 83, andbandpass filters 53, 69 and 85. In other embodiments, a common amplifieramplifies the EEG signal prior to filters 53, 69 and 85. Bandpass filter53 allows frequencies between approximately 4 Hz and approximately 8 Hz,and signals within the frequency range may be prevalent in the EEGduring S1 and S2 sleep states. Bandpass filter 69 allows frequenciesbetween approximately 1 Hz and approximately 3 Hz, which may beprevalent in the EEG during the S3 and S4 sleep states. Bandpass filter85 allows frequencies between approximately 10 Hz and approximately 50Hz, which may be prevalent in the EEG during REM sleep. Each resultingsignal may then processed to identify in which sleep state patient 12Bis in.

After bandpass filtering of the original EEG signal, the filteredsignals are similarly processed in parallel before being delivered tosleep logic module 99. For ease of discussion, only one of the threechannels will be discussed herein, but each of the filtered signals maybe processed similarly.

Once the EEG signal is filtered by bandpass filter 53, the signal isrectified by full-wave rectifier 55. Modules 57 and 59 respectivelydetermine the foreground average and background average so that thecurrent energy level can be compared to a background level at comparator63. The signal from background average is increased by gain 61 beforebeing sent to comparator 63, because comparator 63 operates in the rangeof millivolts or volts while the EEG signal amplitude is originally onthe order of microvolts. The signal from comparator 63 is indicative ofsleep stages S1 and S2. If duration logic 65 determines that the signalis greater than a predetermined level for a predetermined amount oftime, the signal is sent to sleep logic module 99 indicating thatpatient 12 may be within the S1 or S2 sleep states. In some embodiments,as least duration logic 65, 81, 97 and sleep logic 99 may be embodied ina processor of the device containing EEG module 49.

Module 49 may detect all sleep types for patient 12. Further, thebeginning of sleep may be detected by module 49 based on the sleep stateof patient 12. Some of the components of module 49 may vary from theexample of FIG. 3. For example, gains 61, 77 and 93 may be provided fromthe same power source. Module 49 may be embodied as analog circuitry,digital circuitry, or a combination thereof

In other embodiments, module 49 may not need to reference the backgroundaverage to determine the current state of sleep of patient 12. Instead,the power of the signals from bandpass filters 53, 69 and 85 arecompared to each other, and sleep logic module 99 determines which thesleep state of patient 12 based upon the frequency band that has thehighest power. In this case, the signals from full-wave rectifiers 55,71 and 87 are sent directly to a device that calculates the signalpower, such as a spectral power distribution module (SPD), and then tosleep logic module 99 which determines the frequency band of thegreatest power, e.g., the sleep state of patient 12B. In some cases, thesignal from full-wave rectifiers 55, 71 and 87 may be normalized by again component to correctly weight each frequency band.

FIG. 4 illustrates memory 48 of IMDs 14 in greater detail. As shown inFIG. 4, memory 48 stores information describing a plurality of therapyparameter sets 60. Therapy parameter sets 60 may include parameter setsspecified by a clinician using clinician programmer 20. Therapyparameter sets 60 may also include parameter sets that are the result ofa patient 12 changing one or more parameters of one of the preprogrammedtherapy parameter sets. For example, a patient 12 may change parameterssuch as pulse amplitude, frequency or pulse width.

Memory 48 also stores postures 62 or postural transitions identified byprocessor 46. When processor 46 identifies a posture 62 or posturaltransition as discussed above, processor 46 associates the posture orpostural transition with the current one of therapy parameter sets 60,e.g., the one of therapy parameter sets 60 that processor 46 iscurrently using to control delivery of therapy by therapy module 44 to apatient 12. For example, processor 46 may store determined postures 62within memory 48 with an indication of the parameter sets 60 with whichthey are associated. In other embodiments, processor 46 stores samples(not shown) of signals generated by sensors 40 as a function of posturewithin memory 48 with an indication of the parameter sets 60 with whichthey are associated.

Memory 48 also stores the activity levels 64 determined by processor 46.When processor 46 determines an activity level as discussed above,processor 46 associates the determined activity level 64 with thecurrent therapy parameter set 60, e.g., the one of therapy parametersets 60 that processor 46 is currently using to control delivery oftherapy by therapy module 44 to a patient 12. In some embodiments, forexample, processor 46 may store determined activity levels 64 withinmemory 48 with an indication of the posture 62 and parameter sets 60with which they are associated. In other embodiments, processor 46stores samples (not shown) of signals generated by sensors 40 as afunction of patient activity within memory 48 with an indication of theposture 62 and parameter sets 60 with which they are associated.

In some embodiments, processor 46 determines a value of one or moreactivity metrics for each of therapy parameter sets 60 based on theactivity levels 64 associated with the parameter sets 60. In suchembodiments, processor 46 may store the determined activity metricvalues 70 within memory 48 with an indication as to which of therapyparameter sets 60 the determined values are associated with. Forexample, processor 46 may determine a mean or median of activity levelsassociated with a therapy parameter set, and store the mean or medianactivity level as an activity metric value 70 for the therapy parameterset.

In embodiments in which activity levels 64 comprise activity counts,processor 46 may store, for example, an average number of activitycounts per unit time as an activity metric value. An average number ofactivity counts over some period substantially between ten and sixtyminutes, for example, may provide a more accurate indication of activitythan an average over shorter periods by ameliorating the effect oftransient activities on an activity signal or physiological parameters.For example, rolling over in bed may briefly increase the amplitude ofan activity signal and a heart rate, possibly skewing the efficacyanalysis.

In other embodiments, processor 46 may compare a mean or median activitylevel to one or more threshold values, and may select an activity metricvalue from a predetermined scale of activity metric values based on thecomparison. The scale may be numeric, such as activity metric valuesfrom 1-10, or qualitative, such as low, medium or high activity. Thescale of activity metric values may be, for example, stored as a look-uptable within memory 48. Processor 46 stores the activity metric value 70selected from the scale within memory 48.

In some embodiments, processor 46 compares each activity level 64associated with a therapy parameter set 60 to one or more thresholdvalues. Based on the comparison, processor 46 may determine percentagesof time above and/or below the thresholds, or within threshold ranges.Processor 46 may store the one or more determined percentages withinmemory 48 as one or more activity metric values 70 for that therapyparameter set. In other embodiments, processor 46 compares each activitylevel 64 associated with a therapy parameter set 60 to a thresholdvalues, and determines an average length of time that consecutivelyrecorded activity levels 64 remained above the threshold as an activitymetric value 70 for that therapy parameter set.

In some embodiments, processor 46 determines a plurality of activitymetric values for each of the plurality of therapy parameter sets, anddetermines an overall activity metric value for a parameter set based onthe values of the individual activity metrics for that parameter set.For example, processor 46 may use the plurality of individual activitymetric values as indices to identify an overall activity metric valuefrom a look-up table stored in memory 48. Processor 46 may select theoverall metric value from a predetermined scale of activity metricvalues, which may be numeric, such as activity metric values from 1-10,or qualitative, such as low, medium or high activity.

Further, as discussed above, processor 46 may identify the plurality ofpostures assumed by a patient 12 over the times that a therapy parameterset was active based on the postures 62 associated with that therapyparameter set. In such embodiments, processor 46 may determine aplurality of values of an activity metric for each therapy parameter setand posture, e.g., a value of the activity metric for each parameterset/posture pair. Processor 46 may determine an activity metric value 70for a parameter set/posture pair based on the activity levels 64associated with the therapy parameter set and the posture, e.g., theactivity levels 64 collected while that therapy parameter set was activeand the a patient 12 was in that posture.

In some embodiments, processor 46 also determines a value of one or moreposture metrics for each of therapy parameter sets 60 based on thepostures 62 associated with the parameter sets 60. Processor 46 maystore the determined posture metric values 68 within memory 48 with anindication as to which of therapy parameter sets 60 the determinedvalues are associated with. For example, processor 46 may determine anamount of time that a patient 12 was in a posture when a therapyparameter set 60 was active, e.g., an average amount of time over aperiod of time such as an hour, as a posture metric 68 for the therapyparameter set 60. Processor 46 may additionally or alternativelydetermine percentages of time that a patient 12 assumed one or morepostures while a therapy parameter set was active as a posture metric 68for the therapy parameter set 60. As another example, processor 46 maydetermine an average number of transitions over a period of time, suchas an hour, when a therapy parameter set 60 was active as a posturemetric 68 for the therapy parameter set 60.

In some embodiments, processor 46 determines a plurality of posturemetric values for each of the plurality of therapy parameter sets 60,and determines an overall posture metric value for a parameter set basedon the values of the individual posture metrics for that parameter set.For example, processor 46 may use the plurality of individual posturemetric values as indices to identify an overall posture metric valuefrom a look-up table stored in memory 48. Processor 46 may select theoverall posture metric value from a predetermined scale of posturemetric values, which may be numeric, such as posture metric values from1-10.

The various thresholds described above as being used by processor 46 todetermine activity levels 62, postures 64, posture metric values 68, andactivity metric values 70 may be stored in memory 48 as thresholds 66,as illustrated in FIG. 4. In some embodiments, threshold values 66 maybe programmable by a user, e.g., a clinician, using one of programmers20, 26. Further, the clinician may select which activity metric values70 and posture metric values 68 are to be determined via one ofprogrammers 20, 26.

As shown in FIGS. 2A and 2B, IMDs 14 include a telemetry circuit 50, andprocessor 46 communicates with programmers 20, 26, or another computingdevice, via telemetry circuit 50. In some embodiments, processor 46provides information identifying therapy parameter sets 60, postures 62,posture metric values 68, and activity metric values 70 associated withthe parameter sets to one of programmers 20, 26, or the other computingdevice, and the programmer or other computing device displays a list oftherapy parameter sets 60 and associated postures 62 and metric values68, 70. In other embodiments, as will be described in greater detailbelow, processor 46 does not determine metric values 68, 70. Instead,processor 46 provides postures 62 and activity levels 64 to theprogrammer 20, 26 or other computing device via telemetry circuit 50,and the programmer or computing device determines metric values 68, 70for display to the clinician. Further, in other embodiments, processor46 provides samples of signals generated by sensors 40 to the programmer20, 26 or other computing device via telemetry circuit 50, and theprogrammer or computing device may determine postures 62, activitylevels 64, and metric values 68, 70 based on the samples. Some externalmedical device embodiments of the invention include a display, and aprocessor of such an external medical device may both determine metricvalues 68, 70 and display a list of therapy parameter sets 60 andassociated metric values to a clinician.

FIG. 5 is a flow diagram illustrating an example method for collectingposture and activity information that may be employed by an IMD 14. AnIMD 14 monitors one or more signals generated by sensors 40 (80). Forexample, an IMD 14 may monitor signals generated by a plurality oforthogonally aligned accelerometers, as described above. Each of theaccelerometers may be substantially aligned with a respective axis ofthe body of a patient 12.

An IMD 14 identifies a posture 62 (82). For example, the IMD 14 mayidentify a current posture of a patient 12 at a time when the signalsgenerated by sensors 40 are sampled, or may identify the occurrence of atransition between postures. The IMD 14 also determines an activitylevel 64 (84). For example, the IMD 14 may determine a number ofactivity counts based on the one or more of the accelerometer signals,as described above.

An IMD 14 identifies the current therapy parameter set 60, andassociates the identified posture 62 with the current therapy parameterset 60 (86). For example, an IMD 14 may store information describing theidentified posture 62 within memory 48 with an indication of the currenttherapy parameter set 60. An IMD 14 also associates the determinedactivity level 64 with the posture a patient 12 is currently in, e.g.,the most recently identified posture 62, and the current therapyparameter set 60 (86). For example, an IMD 14 may store the determinedactivity level 64 in memory 48 with an indication of the current posture62 and therapy parameter set 60. An IMD 14 may then update one or moreposture and/or activity metric values 68, 70 associated with the currenttherapy parameter set 60 and posture 62, e.g., the current therapyparameter set/posture pair, as described above (88).

An IMD 14 may periodically perform the example method illustrated inFIG. 5, e.g., may periodically monitor the signals generated by sensors40 (80), determine postures 62 and activity levels 64 (82, 84), andassociate the determined postures 62 and activity levels 64 with acurrent therapy parameter set 60 (86). Postures 62 and activity levels64 need not be determined with the same frequency. Further, as describedabove, an IMD 14 may only perform the example method during daytimehours, or when patient is awake and not attempting to sleep, and/or onlyin response to an indication received from a patient 12 via patientprogrammer 20. Additionally, an IMD 14 need not update metric values 68,70 each time a posture 62 or activity level 64 is determined. In someembodiments, for example, an IMD 14 may store postures 62 and activitylevels 64 within memory 48, and may determine the metric values 68, 70upon receiving a request for the values from one of programmers 20, 26.

Further, in some embodiments, as will be described in greater detailbelow, an IMD 14 does not determine the metric values 68, 70, butinstead provides postures 62 and activity levels 64 to a computingdevice, such as clinician programmer 20 or patient programmer 26. Insuch embodiments, the computing device determines the metric valuesassociated with each of the therapy parameter set/posture pair.Additionally, as described above, an IMD 14 need not determine postures62 and activity levels 64, but may instead store samples of the signalsgenerated by sensors 40. In such embodiments, the computing device maydetermine postures, activity levels, and metric values based on thesamples.

FIG. 6 is a flow diagram illustrating an example method for collectingactivity information based on patient posture that may be employed by anIMD 14. In some embodiments, an IMD 14 need not store postures 62,determine posture metrics 68, or associate activity levels 64 withparticular postures. Rather, as illustrated in FIG. 6, an IMD 14 maylimit activity information collection, e.g., determination of activitylevels 64, to times when a patient 12 is in a target posture, e.g., aposture of interest. A target posture may be, for example, upright,e.g., standing or sitting, or may be only standing. In some cases, theactivity of a patient 12 while in such target postures may beparticularly indicative of the effectiveness of a therapy.

An IMD 14 monitors one or more signals generated by sensors 40 (90). Forexample, an IMD 14 may monitor signals generated by a plurality oforthogonally aligned accelerometers, as described above. Each of theaccelerometers may be substantially aligned with a respective axis ofthe body of a patient 12.

An IMD 14 determines whether a patient 12 is upright based upon thesignals (92). If patient a 12 is upright, IMD 14 determines an activitylevel 64 (94), and associates the determined activity level 64 with acurrent set of therapy parameters 60 (96). For example, an IMD 14 maydetermine a number of activity counts based on the one or more of theaccelerometer signals, as described above, and may store the determinedactivity level 64 in memory 48 with an indication of the current therapyparameter set 60. An IMD 14 may then update one or more activity metricvalues 68 associated with the current therapy parameter set 60 (98).

As is the case with the example method illustrated in FIG. 5, an IMD 14may periodically perform the example method illustrated in FIG. 6, e.g.,may periodically monitor the signals generated by sensors 40 (90),determine whether a patient 12 is in a posture of interest (92),determine activity levels 64 when a patient 12 is in the posture ofinterest (94), and associate the determined activity levels 64 with acurrent therapy parameter set 60 (96). Further, as described above, anIMD 14 may only perform the example method during daytime hours, or whenpatient is awake and not attempting to sleep, and/or only in response toan indication received from a patient 12 via patient programmer 20.Additionally, an IMD 14 need not update activity metric values 70 eachtime an activity level 64 is determined. In some embodiments, forexample, an IMD 14 may store activity levels 64 within memory, and maydetermine the activity metric values 70 upon receiving a request for thevalues from one of programmers 20, 26.

Further, in some embodiments, as will be described in greater detailbelow, an IMD 14 does not determine the activity metric values 70, butinstead provides activity levels 64 to a computing device, such asclinician programmer 20 or patient programmer 26. In such embodiments,the computing device determines the activity metric values associatedwith each of the therapy parameter sets. Additionally, as describedabove, an IMD 14 need not determine postures 62 and activity levels 64,but may instead store samples of the signals generated by sensors 40. Insuch embodiments, the computing device may determine postures, activitylevels, and activity metric values based on the samples.

FIG. 7 is a block diagram illustrating clinician programmer 20. Aclinician may interact with a processor 100 via a user interface 102 inorder to program therapy for a patient 12, e.g., specify therapyparameter sets. Processor 100 may provide the specified therapyparameter sets to an IMD 14 via telemetry circuit 104.

At another time, e.g., during a follow up visit, processor 100 mayreceive information identifying a plurality of therapy parameter sets 60from an IMD 14 via telemetry circuit 104, which may be stored in amemory 106. The therapy parameter sets 60 may include the originallyspecified parameter sets, and parameter sets resulting from manipulationof one or more therapy parameters by a patient 12 using patientprogrammer 26. In some embodiments, processor 100 also receives postureand activity metric values 68, 70 associated with the therapy parametersets 60, and stores the metric values in memory 106. In otherembodiments, processor 100 may receive postures 62 and activity levels64 associated with the therapy parameter sets 60, and determine values68, 70 of one or more metrics for each of the plurality of therapyparameter sets 60 using any of the techniques described above withreference to an IMD 14 and FIGS. 2A, 2B and 4. In still otherembodiments, processor 100 receives samples of signals generated bysensors 40, either from an IMD 14, from a separate monitor that includesor is coupled to sensors 40, or directly from sensors 40, and determinespostures 62, activity levels 64 and metric values 68, 70 based onsignals using any of the techniques described above with reference tothe IMD 14 and FIGS. 2A, 2B and 4.

Upon receiving or determining posture and activity metric values 68, 70,processor 100 may generate a list of the therapy parameter sets 60 andassociated metric values 68, 70, and present the list to the clinician.User interface 102 may include display 22, and processor 100 may displaythe list via display 22. The list of therapy parameter sets 60 may beordered according to a metric value, and where a plurality of metricvalues are associated with each of the parameter sets, the list may beordered according to the values of the metric selected by the clinician.Processor 100 may also present other posture or activity information toa user, such as a trend diagram of activity or posture over time, or ahistogram, pie chart, or other illustration of percentages of time thata patient 12 was within certain postures 62, or activity levels 64 werewithin certain ranges. Processor 100 may generate such charts ordiagrams using postures 62 and activity levels 64 associated with aparticular one of the therapy parameter sets 60, or all of the postures62 and activity levels 64 recorded by an IMD 14.

User interface 102 may include display 22 and keypad 24, and may alsoinclude a touch screen or peripheral pointing devices as describedabove. Processor 100 may include a microprocessor, a controller, a DSP,an ASIC, an FPGA, discrete logic circuitry, or the like. Memory 106 mayinclude program instructions that, when executed by processor 100, causeclinician programmer 20 to perform the functions ascribed to clinicianprogrammer 20 herein. Memory 106 may include any volatile, non-volatile,fixed, removable, magnetic, optical, or electrical media, such as a RAM,ROM, CD-ROM, hard disk, removable magnetic disk, memory cards or sticks,NVRAM, EEPROM, flash memory, and the like.

FIG. 8 illustrates an example list 110 of therapy parameter sets 60 andassociated metric values 68, 70 that may be presented by clinicianprogrammer 20. Each row of example list 110 includes an identificationof one of therapy parameter sets 60, the parameters of the therapyparameter set, and an identification of the postures assumed by apatient 12 when the parameter set was active, e.g., the categories ofpostures 62 associated with the parameter set. In the illustratedexample, each of the listed therapy parameter sets 60 is associated withtwo postural categories, i.e., upright and recumbent.

Each of the listed therapy parameter sets is also associated with twovalues 70 for each of two activity metrics, i.e., an activity metricvalue 70 for each posture associated with the therapy parameter set. Theactivity metrics illustrated in FIG. 8 are a percentage of time active,and an average number of activity counts per hour. An IMD 14 orprogrammer 20 may determine the average number of activity counts perhour for one of the illustrated therapy parameter set/posture pairs byidentifying the total number of activity counts associated with theparameter set and the posture, and the total amount of time that patientwas in that posture while the IMD 14 was using the parameter set. An IMD14 or programmer 20 may determine the percentage of time active for oneof the illustrated therapy parameter set/posture pairs by comparing eachactivity level associated with the parameter set and posture to an“active” threshold, and determining the percentage of activity levelsabove the threshold. As illustrated in FIG. 8, an IMD 14 or programmer20 may also compare each activity level for the therapyparameter/posture pair set to an additional, “high activity” threshold,and determine a percentage of activity levels above that threshold.

As illustrated in FIG. 8, list 110 may also include a posture metric 68.In the illustrated example, list 110 includes as posture metrics 68 foreach therapy parameter set the percentage of time that patient 12 was ineach posture when the therapy parameter set was active. Programmer 20may order list 110 according to a user-selected one of the metrics 68,70.

FIG. 9 is a flow diagram illustrating an example method for displaying alist of therapy parameter sets 60 and associated metric values 68, 70that may be employed by a clinician programmer 20. Although describedwith reference to clinician programmer 20, patient programmer 26 oranother computing device may perform the method illustrated by FIG. 7.

Programmer 20 receives information identifying therapy parameter sets 60and associated postures 62 and activity levels 64 from an IMD 14 (120).Programmer 20 then determines one or more posture and activity metricvalues 68, 70 for each of the therapy parameter sets based on thepostures 62 and activity levels 64 associated with the therapy parametersets (122). In other embodiments, an IMD 14 determines the metricvalues, and provides them to programmer 20, or provides samples ofsignals associated with therapy parameter sets to programmer 20 fordetermination of metric values, as described above. After receiving ordetermining metric values 68, 70, programmer 20 presents a list 110 oftherapy parameter sets 60 and associated metric values 68, 70 to theclinician, e.g., via display 22 (124). Programmer 20 may order list 110of therapy parameter sets 60 according to the associated metric values,and the clinician may select according to which of a plurality ofmetrics list 110 is ordered via a user interface 82 (126).

In some embodiments, as discussed above, one or more of an IMD 14,programmers 20, 26, or another computing device may conduct asensitivity analysis of one or more posture and/or activity metricvalues 68, 70 to identify one or more therapy parameter sets for use indelivering therapy to a patient 12. The sensitivity analysis may beperformed as an alternative or in addition to presenting posture andactivity information to a user for evaluation of therapy parameter sets.

The IMD, programmer, or the other computing device may perform thesensitivity analysis to identify a value for each therapy parametersthat defines substantially maximum or minimum posture and/or activitymetric values. In other words, the sensitivity analysis identifiestherapy parameter values that yield the “best” metric values. The IMD,programmer, or other computing device then identifies one or morebaseline therapy parameter sets that include the identified parametervalues, and stores the baseline therapy parameter sets as therapyparameter sets 60 or separately within memory 48 of an IMD 14. An IMD 14may then deliver stimulation according to the baseline therapy parametersets. The baseline therapy parameter sets include the values forrespective therapy parameters that produced the best activity and/orposture metric values.

In some embodiments, the IMD, programmer, or other computing device mayadjust the therapy delivered by an IMD 14 based on a change in theactivity or posture metric values 68, 70. In particular, the IMD,programmer, or other computing device may perturb one or more therapyparameters of a baseline therapy parameter set, such as pulse amplitude,pulse width, pulse rate, duty cycle, and duration, to determine if thecurrent posture and/or activity metric values improve or worsen duringperturbation. In some embodiments, values of the therapy parameters maybe iteratively and incrementally increased or decreased untilsubstantially maximum or minimum values of the posture and/or activitymetric are again identified.

FIG. 10 is a flow diagram illustrating an example method for identifyinga therapy parameter set, e.g., a baseline therapy parameter set, basedon collected posture and/or activity information that may be employed byan IMD 14. For ease of description, a number of the actions that arepart of the method illustrated in FIG. 10 are described as beingperformed by an IMD 14. However, in some embodiments, as discussedabove, an external computing device, such as one of programmers 20, 26,and more particularly the processor of such a computing device, mayperform one or more of the activities attributed to an IMD 14 below.

An IMD 14 receives a therapy parameter range for therapy parameters(130) from a clinician using clinician programmer 20 via telemetrycircuit 50. The range may include minimum and maximum values for each ofone or more individual therapy parameters, such as pulse amplitude,pulse width, pulse rate, duty cycle, duration, dosage, infusion rate,electrode placement, and electrode selection. The range may be stored inmemory 48, as described in reference to FIG. 4.

Processor 46 then randomly or non-randomly generates a plurality oftherapy parameter sets 60 with individual parameter values selected fromthe range (132). The generated therapy parameter sets 60 maysubstantially cover the range, but do not necessarily include each andevery therapy parameter value within the therapy parameter range, orevery possible combination of therapy parameters within the range. Thegenerated therapy parameter sets 60 may also be stored in memory 48.

An IMD 14 monitors at least one posture or activity metric 68, 70 of apatient 12 for each of the randomly or non-randomly generated therapyparameter sets 60 spanning the range (134). The values of the metricscorresponding to each of the therapy parameter sets 60 may be stored inmemory 48 of an IMD 14, as described above. An IMD 14 then conducts asensitivity analysis of the one or more posture and/or activity metricsfor each of the therapy parameters, e.g., each of pulse amplitude, pulsewidth, pulse rate and electrode configuration (136). The sensitivityanalysis determines a value for each of the therapy parameters thatproduced a substantially maximum or minimum value of the one or moremetrics. One or more baseline therapy parameter sets are then determinedbased on the therapy parameter values identified by the sensitivityanalysis (138). The baseline therapy parameter sets include combinationsof the therapy parameter values individually observed to producesubstantially maximum or minimum values of the one or more posture oractivity metrics 68, 70. The baseline therapy parameter sets may also bestored with therapy parameters sets 60 in memory 48. In someembodiments, the baseline therapy parameter sets may be storedseparately from the generated therapy parameter sets.

After this initial baseline therapy parameter set identification phaseof the example method, an IMD 14 may control delivery of the therapybased on the baseline therapy parameter sets. Periodically during thetherapy, an IMD 14 checks to ensure that the baseline therapy parametersets continues to define substantially maximum or minimum posture and/oractivity metric values for a patient 12. An IMD 14 first perturbs atleast one of the therapy parameter values of a baseline therapyparameter set (140). The perturbation comprises incrementally increasingand/or decreasing the therapy parameter value, or changing electrodepolarities. A perturbation period may be preset to occur at a specifictime, in response to a physiological parameter monitored by the IMD, orin response to a signal from the patient or clinician. The perturbationmay be applied for a single selected parameter or two or moreparameters, or all parameters in the baseline therapy parameter set.Hence, numerous parameters may be perturbed in sequence. For example,upon perturbing a first parameter and identifying a value that producesa maximum or minimum metric value, a second parameter may be perturbedwith the first parameter value fixed at the identified value. Thisprocess may continue for each of the parameters in a baseline therapyparameter set, and for each of a plurality of baseline therapy parametersets.

Upon perturbing a parameter value, an IMD 14 then compares a value ofthe one or more metrics defined by the perturbed therapy parameter setto a corresponding value of the metric defined by the baseline therapyparameter set during the initial baseline identification phase (142). Ifthe metric values do not improve with the perturbation, an IMD 14maintains the unperturbed baseline therapy parameter set values (144).If the metric values do improve with the perturbation, an IMD 14perturbs the therapy parameter value again (146) in the same directionthat defined the previous improvement in the metric values. An IMD 14compares a value of the metrics defined by the currently perturbedtherapy parameter set to the metric values defined by the therapyparameter set of the previous perturbation (148). If the metric valuesdo not improve, an IMD 14 updates the baseline therapy parameter setbased on the therapy parameter values from the previous perturbation(150). If the metric values improve again, an IMD 14 continues toperturb the therapy parameter value (146).

Periodically checking the values of one or more metrics for the baselinetherapy parameter set during this perturbation phase of the examplemethod allows an IMD 14 to consistently deliver a therapy to a patient12 that defines a substantially maximum or minimum posture and/oractivity metric values 68, 70. This may allow the patient's symptoms tobe continually managed even as the patient's physiological parametersand symptoms change.

Various embodiments of the invention have been described. However, oneskilled in the art will recognize that various modifications may be madeto the described embodiments without departing from the scope of theinvention. For example, the invention may be embodied as acomputer-readable medium that includes instructions to cause a processorto perform any of the methods described herein.

As another example, although described herein primarily in the contextof treatment with an implantable neurostimulator, the invention is notso limited. The invention may be embodied in any implantable medicaldevice that delivers a therapy, such as a cardiac pacemaker or animplantable pump. Further, the invention may be implemented via anexternal, e.g., non-implantable, medical device. In such embodiments,the external medical device itself may include a user interface anddisplay to present activity information to a user, such as a clinicianor patient, for evaluation of therapy parameter sets.

As discussed above, the overall activity level of a patient, e.g., theextent to which the patient is on his or her feet and moving orotherwise active, rather than sitting or lying in place, may benegatively impacted by any of a variety of ailments or symptoms.Accordingly, the activity level, postures and posture change frequencyof a patient may reflect the progression, status, or severity of theailment or symptom. Further, the extent that a patient is active andupright may reflect the efficacy of a particular therapy or therapyparameter set in treating the ailment or symptom. In other words, it maygenerally be the case that the more efficacious a therapy or therapyparameter set is, the more active and upright a patient will be.

As discussed above, in accordance with the invention, activity andposture metrics may be monitored, and used to evaluate the status,progression or severity of an ailment or symptom, or the efficacy oftherapies or therapy parameter sets used to treat the ailment orsymptom. As an example, chronic pain chronic pain may cause a patient toavoid particular activities, high levels of activity, or activity ingeneral. Systems according to the invention may monitor activity andactivity metrics to evaluate the extent to which the patient isexperiencing pain.

In some embodiments, systems according to the invention may include anyof a variety of medical devices that deliver any of a variety oftherapies to treat chronic pain, such as SCS, DBS, cranial nervestimulation, peripheral nerve stimulation, or one or more drugs. Systemsmay use the techniques of the invention described above to determineactivity and posture metrics for the patient and evaluate suchtherapies, e.g., by associating values for the metric with therapyparameter sets for delivery of such therapies. Systems according to theinvention may thereby evaluate the extent to which a therapy or therapyparameter set is alleviating chronic pain by evaluating the extent towhich the therapy or therapy parameter set allows the patient to be moreactive or engage in particular activities or postures.

As another example, psychological disorders may cause a patient to beless active and more recumbent. Accordingly, embodiments of theinvention may determine activity and posture metrics to track the statusor progression of a psychological disorder, such as depression, mania,bipolar disorder, or obsessive-compulsive disorder. Further, systemsaccording to the invention may include any of a variety of medicaldevices that deliver any of a variety of therapies to treat apsychological disorder, such as DBS, cranial nerve stimulation,peripheral nerve stimulation, vagal nerve stimulation, or one or moredrugs. Systems may use the techniques of the invention described aboveto associate activity and posture metric values with the therapies ortherapy parameter sets for delivery of such therapies, and therebyevaluate the extent to which a therapy or therapy parameter set isalleviating the psychological disorder by evaluating the extent to whichthe therapy parameter set improves the overall activity level of thepatient, as indicated by activity and posture.

Movement disorders, such as tremor, Parkinson's disease, multiplesclerosis, epilepsy, and spasticity may also affect the overall activitylevel of a patient, as well as posture. Further, movement disorders arealso characterized by irregular, uncontrolled and generallyinappropriate movements, e.g., tremor or shaking, particularly of thelimbs. In addition to using the sensors described above to sense theoverall activity level of a movement disorder patient, some embodimentsof the invention may use such sensors to detect the types ofinappropriate movements associated with the movement disorder. Forexample, accelerometers, piezoelectric crystals, or EMG electrodeslocated in the trunk or limbs of a patient may be able to detectinappropriate movements such as tremor or shaking Movement disorders andpsychological disorders are examples of neurological disorders that maybe treated according to the therapy and therapy evaluation describedherein.

Systems according to the invention may periodically determine the levelor severity of such movements based on the signals output by suchsensors, associate the inappropriate movement levels with currenttherapy parameter sets, and determine activity metric values for therapyparameter sets based on the associated levels. For example, a processorof such a system may determine a frequency or amount of time that suchmovements exceeded a threshold during delivery of a therapy parameterset as an inappropriate movement based activity metric value for thetherapy parameter set.

Another activity-related movement disorder symptom that is relativelyspecific to Parkinson's disease is “gait freeze.” Gait freeze may occurwhen a Parkinson's patient is walking Gait freeze refers to a relativelysudden inability of a Parkinson's patient to take further steps. Gaitfreeze is believed to result from a neurological failure and, morespecifically, a failure in the neurological signaling from the brain tothe legs.

In some embodiments, in addition to the activity metrics describedabove, any of the devices or processors described above may additionallyidentify gait freeze events based on the signals output by sensors 40.For example, processor 46, or another processor of the system, maydetect a relatively sudden cessation of activity associated with a gaitevent based on the output of accelerometers, piezoelectric crystals, EMGelectrodes, or other sensors that output signals based on footfalls orimpacts associated with, for example, walking When experiencing a gaitfreeze event, a patient may “rock” or “wobble” while standing in place,as if attempting unsuccessfully to move. In some embodiments, processor46 may monitor any of sensors 40 that output signals as a function ofposture discussed above, such as a 3-axis accelerometer, to detect theminor, rhythmic changes in posture associated with rocking or wobbling.Processor 46 may detect a gait freeze event as when it occurs based onone or more of the posture or activity sensors. For example, processor46 may confirm that a relatively sudden cessation of activity is in facta gait freeze event based on rocking or wobbling indicated by posturesensors.

In some embodiments, the processor may detect a gait freeze prior toonset. For example, sensors 40 may include EMG or EEG electrodes, andprocessor 46 may detect a gait freeze prior to onset based on irregularEMG or EEG activity. EMG signals, as an example, demonstrateirregularity just prior to a freezing episode, and a processor maydetect this irregularity as being different from the EMG signalstypically associated with walking In other words, a walking patient mayexhibit normal EMG pattern in the legs, which may be contrasted with EMGactivity and timing changes that precede freezing.

In general, EMG signals from right and left leg muscles include aregularly alternating rhythm pattern that characterizes normal gait.When the “timing” of the pattern fails, there is no longer a regularrhythm, and a gait freeze may result. Accordingly, a processor maydetect irregularity, variability, or asymmetry, e.g., within and betweenright and left leg muscles, in one or more EMG signals, and may detectan oncoming gait freeze prior to occurrence based on the detection. Insome embodiments, the processor may compare the EMG signals to one ormore thresholds to detect gait freeze. Comparison to a threshold may,for example, indicate an absolute value or increase in irregularity,variability, asymmetry that exceeds a threshold, indicating an oncominggait freeze. In some embodiments, thresholds may be determined based onEMG signal measurements made when the patient is walking normally.

Whether or not gait freeze is detected prior to r during occurrence, theprocessor may associate the occurrence of the gait freeze event with acurrent therapy parameter set used to control delivery of a therapy forParkinson's disease, such as DBS or a drug. Additionally, the processormay determine or update an activity metric value for the therapyparameter set based on the gait freeze event, such as a total number ofgait freeze events for the therapy parameter set, or an average numberof gait freeze events over a period of time.

Systems according to the invention may include any of a variety ofmedical devices that deliver any of a variety of therapies to treatmovement disorders, such as DBS, cortical stimulation, or one or moredrugs. Baclofen, which may or may not be intrathecally delivered, is anexample of a drug that may be delivered to treat movement disorders.Systems may use the techniques of the invention described above toassociate any of the above-described sleep quality or activity metricswith therapies or therapy parameter sets for delivery of such therapies.In this manner, such systems may allow a user to evaluate the extent towhich a therapy or therapy parameter set is alleviating the movementdisorder by evaluating the extent to which the therapy parameter setimproves the sleep quality, general activity level, inappropriateactivity level, or number of gait freezes experienced by the patient.

Further, many of the ailments and symptoms described above, includingmovement disorders and chronic pain, may more generally affect the gaitof a patient. More particularly, such symptoms and ailments may resultin, as examples, an arrhythmic, asymmetric (left leg versus right leg),or unusually variable gait, or a gait with relative short stridelengths. Systems according to the invention may use sensors discussedabove that output signals as a function of activity, and particularly asa function of footfalls or impacts, to monitor gait.

For example, a processor of such a system may periodically determine avalue for asymmetry, variability, or stride length of gait, andassociated such values with a current therapy parameter set used deliverany of the therapies discussed herein with reference to chronic pain ormovement disorders. The processor may determine an activity metric valuebased on gait by, for example, averaging the gait values associated witha therapy parameter set over a period of time, such as a day, week ormonth. The processor of the system that performs the techniques of theinvention, such as gait monitoring and activity metric determination,may include one or more of a processor of an IMD or a processor of aprogramming or computing device, as discussed above.

Additionally, the invention is not limited to embodiments in which aprogramming device receives information from the medical device, orpresents information to a user. Other computing devices, such ashandheld computers, desktop computers, workstations, or servers mayreceive information from the medical device and present information to auser as described herein with reference to programmers 20, 26. Acomputing device, such as a server, may receive information from themedical device and present information to a user via a network, such asa local area network (LAN), wide area network (WAN), or the Internet.Further, in some embodiments, the medical device is an external medicaldevice, and may itself include user interface and display to presentactivity information to a user, such as a clinician or patient, forevaluation of therapy parameter sets.

As another example, the invention may be embodied in a trialneurostimulator, which is coupled to percutaneous leads implanted withinthe patient to determine whether the patient is a candidate forneurostimulation, and to evaluate prospective neurostimulation therapyparameter sets. Similarly, the invention may be embodied in a trial drugpump, which is coupled to a percutaneous catheter implanted within thepatient to determine whether the patient is a candidate for animplantable pump, and to evaluate prospective therapeutic agent deliveryparameter sets. Posture and activity metric values collected during useof the trial neurostimulator or pump may be used by a clinician toevaluate the prospective therapy parameter sets, and select parametersets for use by the later implanted non-trial neurostimulator or pump.The posture and activity metric values may be collected by the trialdevice in the manner described above with reference to an IMD 14, or bya programmer 20, 26 or other computing device, as described above. Aftera trial period, a programmer or computing device may present a list ofprospective parameter sets and associated metric values to a clinician.The clinician may use the list to identify potentially efficaciousparameter sets, and may program a permanent implantable neurostimulatoror pump for the patient with the identified parameter sets.

In some embodiments, a trial neurostimulator or pump, or a programmer orother external computing device, may perform a sensitivity analysis asdescribed above on a range of therapy parameters tested by the trialneurostimulator or pump during a trialing period. A permanentimplantable neurostimulator or pump may be programmed with the one ormore baseline therapy parameter sets identified by the sensitivityanalysis, and may periodically perturb the baseline therapy parametersets to maintain effective therapy in the manner described above.

Additionally, as discussed above, the invention is not limited toembodiments in which the therapy delivering medical device monitorsactivity or posture. In some embodiments, a separate monitoring devicemonitors values of one or more physiological parameters of the patientinstead of, or in addition to, a therapy delivering medical device. Themonitor may include a processor 46 and memory 48, and may be coupled toor include sensors 40, as illustrated above with reference to an IMD 14and FIGS. 2A, 2B, and 4.

The monitor may identify postures and activity levels based on thevalues of the monitored physiological parameter values, and determineposture and activity metric values based on the identified postures andactivity levels as described herein with reference to an IMD 14.Alternatively, the monitor may transmit indications of posture andactivity levels to an IMD, programmer, or other computing device, whichmay then determine posture and activity metric values. As anotheralternative, the monitor may transmit recorded physiological parametervalues to an IMD, programmer, or other computing device fordetermination of postures, activity levels, and/or posture and activitymetric values.

FIG. 11 is a conceptual diagram illustrating a monitor 160 that monitorsthe posture and activity of the patient instead of, or in addition to, atherapy delivering medical device. In the illustrated example, monitor160 is configured to be attached to or otherwise carried by a belt 162,and may thereby be worn by patient 12C. FIG. 11 also illustrates varioussensors 40 that may be coupled to monitor 160 by leads, wires, cables,or wireless connections.

In the illustrated example, patient 12C wears an ECG belt 164. ECG belt164 incorporates a plurality of electrodes for sensing the electricalactivity of the heart of patient 12C. The heart rate and, in someembodiments, ECG morphology of patient 12C may monitored by monitor 150based on the signal provided by ECG belt 164. Examples of suitable belts164 for sensing the heart rate of patient 12C are the “M” and “F” heartrate monitor models commercially available from Polar Electro. In someembodiments, instead of belt 160, patient 12C may wear a plurality ofECG electrodes attached, e.g., via adhesive patches, at variouslocations on the chest of the patient, as is known in the art. An ECGsignal derived from the signals sensed by such an array of electrodesmay enable both heart rate and ECG morphology monitoring, as is known inthe art. Signals received from EEG electrodes 174A-C may be analyzed todetermine sleep states, e.g., using techniques and circuitry describedwith reference to FIG. 3.

As shown in FIG. 11, patient 12C may also wear a respiration belt 166that outputs a signal that varies as a function of respiration of thepatient. Respiration belt 166 may be a plethysmograpy belt, and thesignal output by respiration belt 166 may vary as a function of thechanges is the thoracic or abdominal circumference of patient 12C thataccompany breathing by the patient. An example of a suitable belt 166 isthe TSD201 Respiratory Effort Transducer commercially available fromBiopac Systems, Inc. Alternatively, respiration belt 166 may incorporateor be replaced by a plurality of electrodes that direct an electricalsignal through the thorax of the patient, and circuitry to sense theimpedance of the thorax, which varies as a function of respiration ofthe patient, based on the signal. In some embodiments, ECG andrespiration belts 164 and 166 may be a common belt worn by patient 12C,and the relative locations of belts 164 and 166 depicted in FIG. 11 aremerely exemplary.

Monitor 160 may additionally or alternatively include or be coupled toany of the variety of sensors 40 described above with reference to FIGS.2A, 2B, and 4, which output signals that vary as a function of activitylevel or posture. For example, monitor 160 may include or be coupled toa plurality of orthogonally aligned accelerometers, as described above.

FIG. 12 is a conceptual diagram illustrating a monitor that monitorssignals generated by one or more accelerometers instead of, or inaddition to, such monitoring of signals generated by accelerometers orother sensors by a therapy delivering medical device. As shown in FIG.12, patient 12D is wearing monitor 168 attached to belt 170. Monitor 168is capable of receiving measurements from one or more sensors located onor within patient 12D. In the example of FIG. 12, accelerometers 172 and174 are attached to the head and hand of patient 12, respectively.Accelerometers 172 and 174 may measure movement of the extremities, oractivity level, of patient 12 to indicate when the patient moves duringsleep or at other times during the day. Alternatively, more or lessaccelerometers or other sensors may be used with monitor 168.

Accelerometers 172 and 174 may be preferably multi-axis accelerometers,but single-axis accelerometers may be used. As patient 12D moves,accelerometers 172 and 174 detect this movement and send the signals tomonitor 168. High frequency movements of patient 12D may be indicativeof tremor, Parkinson's disease, or an epileptic seizure. Accelerometers172 and 174 may be worn externally, i.e., on a piece or clothing or awatch, or implanted at specific locations within patient 12D. Inaddition, accelerometers 172 and 174 may transmit signals to monitor 168via a wireless or a wired connection.

Monitor 168 may store the measurements from accelerometers 172 and 174in a memory. In some examples, monitor 168 may transmit the measurementsfrom accelerometers 172 and 174 directly to another device, such as anIMD 14 or a programmer. In this case, an the IMD 14 or programmer mayanalyze the measurements from accelerometers 172 and 174 to detectefficacy of therapy, control the delivery of therapy, detect sleep ormonitor sleep quality using any of the techniques described herein.

In some examples, a rolling window of time may be used when analyzingmeasurements from accelerometers 172 and 174. Absolute values determinedby accelerometers 172 and 174 may drift with time or the magnitude andfrequency of patient 12D movement may not be determined by a presetthreshold. For this reason, it may be advantageous to normalize andanalyze measurements from accelerometers 172 and 174 over a discretewindow of time. For example, the rolling window may be useful indetecting epileptic seizures. If monitor 168 or an IMD 14 detects atleast a predetermined number of movements over a 15 second window, anepileptic seizure may be most likely occurring. In this manner, a fewquick movements from patient 12 not associated with a seizure may nottrigger a response, such as recording an incident in a memory or achange in therapy.

FIG. 13 is a flow diagram illustrating monitoring the heart rate andbreathing rate of a patient by measuring cerebral spinal fluid pressure.As discussed above, a physiological parameter that may be measured in apatient 12 is heart rate and respiration, or breathing, rate. In theexample of FIG. 13, cerebral spinal fluid (CSF) pressure may be analyzedto monitor the heart rate and breathing rate of a patient 12. Aclinician initiates a CSF pressure sensor for monitoring heart rateand/or breathing rate (176). Alternatively, the CSF pressure sensor maybe implanted within the brain or spinal cord of a patient 12 to acquireaccurate pressure signals. The CSF pressure sensor may transfer pressuredata to an implanted or external device. As an example used herein, theCSF pressure sensor transmits signal data to an IMD 14.

Once the CSF pressure sensor is initiated, the CSF pressure sensormeasures CSF pressure and transmits the data to an IMD 14 (178). An IMD14 analyzes the CSF pressure signal to identify the heart rate (180) andbreathing rate (182) of a patient 12. The heart rate and breathing ratecan be identified within the overall CSF pressure signal. Higherfrequency fluctuations (e.g. 40 to 150 beats per minute) can beidentified as the heart rate while lower frequency fluctuations (e.g. 3to 20 breaths per minute) in CSF pressure are the breathing rate. An IMD14 may employ filters, transformations, or other signal processingtechniques to identify the heart rate and breathing rate from the CSFpressure signal.

An IMD 14 may utilize the heart rate and breathing rate information whendetermining the activity level of a patient 12, as described above(184). For example, faster heart rates and faster breathing rates mayindicate that the activity level of a patient 12 is higher than normalresting rates. An IMD 14 may then store values of an activity metric,provide the activity metric values to a programmer or other computingdevice, or use them to adjust stimulation therapy (186). As discussedabove, CSF pressure may additionally be used to detect posture, andthereby determine posture metrics.

These and other embodiments are within the scope of the followingclaims.

1. A method for evaluating a neurostimulation therapy delivered to apatient by an implantable medical device system, the method comprising:monitoring a plurality of signals, each of the signals generated by atleast one sensor of the implantable medical device system as a functionof at least one of activity or posture of the patient; determiningwhether the patient is in a target posture based on at least one of thesignals; periodically determining an activity level of the patient basedon at least one of the signals when the patient is in the targetposture; periodically determining values of at least one activity metricbased on the activity levels determined when the patient was in thetarget posture; and displaying for a user the determined activity metricvalues in a manner that is indicative of efficacy of theneurostimulation therapy delivered to the patient.
 2. The method ofclaim 1, wherein the target posture is upright.
 3. The method of claim1, wherein the target posture is standing.
 4. The method of claim 1,wherein the target posture is lying down.
 5. The method of claim 1,wherein displaying for the user the determined activity metric valuescomprises displaying a trend diagram of activity over time based on theactivity metric values determined over time.
 6. The method of claim 1,wherein displaying for the user the determined activity metric valuescomprises displaying a graphical representation of percentages of timethat the activity metric values were within each of a plurality ofranges.
 7. The method of claim 1, wherein displaying for the user thedetermined activity metric values in a manner that is indicative ofefficacy of the neurostimulation therapy delivered to the patientcomprises displaying for the user the determined activity metric valuesin a manner that is indicative of an amount of time that the patient wasupright and active.
 8. The method of claim 1, further comprisingassociating each of the determined activity levels with a therapyparameter set, selected from among a plurality of therapy parametersets, according to which the implantable medical device delivered theneurostimulation therapy to the patient when the activity levels weredetermined, wherein displaying for the user the determined activitymetric values comprises displaying the determined activity metric valuesin a manner that is indicative of the relative efficacy of the pluralityof therapy parameter sets.
 9. The method of claim 1, further comprising:determining an average number of posture transitions over a period oftime; and displaying for the user the determined average number ofposture transitions over the period of time in a manner that isindicative of efficacy of the neurostimulation therapy delivered to thepatient.
 10. The method of claim 1, wherein the neurostimulation therapycomprises at least one of spinal cord stimulation, a movement disordertherapy, a psychological disorder therapy, deep brain stimulation, atremor therapy, a Parkinson's disease therapy, or an epilepsy therapy.11. A medical system comprising: one or more sensors, each of thesensors generating a signal as a function of at least one of activity orposture of a patient; an implantable medical device that delivers aneurostimulation therapy to a patient; and a processor that: determineswhether the patient is in a target posture based on at least one of thesignals, periodically determines an activity level of the patient basedon at least one of the signals when the patient is in the targetposture, and periodically determines values of at least one activitymetric based on the activity levels determined when the patient was inthe target posture; and a computing device that displays for a user thedetermined activity metric values in a manner that is indicative ofefficacy of the neurostimulation therapy delivered to the patient. 12.The medical system of claim 11, wherein the target posture is upright.13. The medical system of claim 11, wherein the target posture isstanding.
 14. The medical system of claim 11, wherein the target postureis lying down.
 15. The medical system of claim 11, wherein the computingdevice displays a trend diagram of activity over time based on theactivity metric values determined over time.
 16. The medical system ofclaim 11, wherein the computing device displays a graphicalrepresentation of percentages of time that the activity metric valueswere within each of a plurality of ranges.
 17. The medical system ofclaim 11, wherein the computing device displays for the user thedetermined activity metric values in a manner that is indicative of anamount of time that the patient was upright and active.
 18. The medicalsystem of claim 11, wherein the processor further comprising associateseach of the determined activity levels with a therapy parameter set,selected from among a plurality of therapy parameter sets, according towhich the implantable medical device delivered the neurostimulationtherapy to the patient when the activity levels were determined, andwherein the computing device displays the determined activity metricvalues in a manner that is indicative of the relative efficacy of theplurality of therapy parameter sets.
 19. The medical system of claim 11,wherein the processor further determines an average number of posturetransitions over a period of time, and wherein the computing devicedisplays for the user the determined average number of posturetransitions over the period of time in a manner that is indicative ofefficacy of the neurostimulation therapy delivered to the patient.
 20. Amedical system comprising: means for monitoring a plurality of signals,each of the signals generated as a function of at least one of activityor posture of the patient; means for determining whether the patient isin a target posture based on at least one of the signals; means forperiodically determining an activity level of the patient based on atleast one of the signals when the patient is in the target posture;means for periodically determining values of at least one activitymetric based on the activity levels determined when the patient was inthe target posture; and means for presenting the determined activitymetric values to a user in a manner that is indicative of efficacy of aneurostimulation therapy delivered to the patient.
 21. Acomputer-readable medium comprising instructions that cause a processorto: monitor a plurality of signals, each of the signals generated by asensor of the implantable medical device system as a function of atleast one of activity or posture of the patient; determine whether thepatient is in a target posture based on at least one of the signals;periodically determine an activity level of the patient based on atleast one of the signals when the patient is in the target posture;periodically determine values of at least one activity metric based onthe activity levels determined when the patient was in the targetposture; and cause display of the determined activity metric values fora user in a manner that is indicative of efficacy of a neurostimulationtherapy delivered to the patient.